In the past, various types of concrete wall forms have been proposed. Some of the proposed forms are designed to be left in place and provide an attachment medium for wall coverings. Many comprise a plurality of modules designed to be assembled together to form a wall. See U.S. Pat. Nos. 3,552,076 entitled CONCRETE FORM; 3,788,020 entitled FOAMED PLASTIC CONCRETE FORM WITH FIRE-RESISTANT TENSION MEMBER; 4,223,501 entitled CONCRETE FORM; and 4,879,855 entitled ATTACHMENT AND REINFORCEMENT MEMBER FOR, MOLDED CONSTRUCTION FORMS. After assembly, concrete is poured into cavities in the form. If desired, reinforcing metal is added prior to pouring the concrete.
While modular concrete forms of the type described in the foregoing United States patents may be usable under some circumstances, they all have disadvantages. Specifically, prior art modular concrete forms have generally been formed of low-density expanded polystyrene (EPS), i.e., polystyrene having a density lying in the 11/2-2 lb./ft..sup.3 range. While low-density polystyrene has adequate insulation properties, it is structurally weak. The strength of expanded polystyrene having a density falling into the 11/2-2 lb./ft..sup.3 range is inadequate to hold screw-type anchors of the type commonly used to attach wall coverings, such as plasterboard and the like. As a result, adhesives must be used to attach wall coverings to concrete forms created entirely from low-density (e.g., 11/2-2lb./ft.sup.3) EPS, i.e., modular forms of the type described in U.S. Pat. No. 3,552,076, referenced above. For a variety of reasons adhesives are not as desirable as mechanical (e.g., screw) anchors.
One proposal designed to overcome the attachment problem described above is to embed attachment strips in side walls formed of EPS. See U.S. Pat. Nos. 4,223,501 and 4,879,855. The most recent of these patents (U.S. Pat. No. 4,879,855) discloses strips of solid galvanized steel attached to expanded webbed steel cross members embedded in EPS side walls. The solid galvanized steel strips are coplanar with the outer surface of the form, and the expanded steel web reinforces the form. Wall coverings are attached by mechanical fasteners to the solid galvanized steel strips.
While this solution partially improves the attachment problem, it has other disadvantages. Specifically, because of the structural dissimilarities between low-density EPS and steel, it is difficult to cut modules having embedded steel elements in order to meet the requirements of a construction job. More specifically, walls in most construction situations have comers. While most comers are 90.degree. comers, occasionally other angles are required. One way of making corners is to cut concrete form modules to fit. As noted above, this is difficult, if not impossible, when the components of a concrete form module have significant structural dissimilarities.
While one could create a variety of comer interlocking concrete modules in the manner described in U.S. Pat. No. 4,879,855, such modules would be expensive to manufacture. In addition, they would increase inventory costs and, in many instances, not be as readily available as desired, leading to construction delays and increased construction costs.
A further disadvantage of interlocking concrete form modules of the type described in U.S. Pat. No. 4,879,855 is the ease of distorting such modules in a construction environment. Because the EPS is only included in side walls and is not integral throughout the entire module, the expanded metal is occasionally bent or the low-density EPS is cracked or broken, resulting in the side walls becoming misaligned.
Another disadvantage of interlocking form modules of the type described in U.S. Pat. No. 4,879,855 is the tendency to lose the galvanized steel attachment strips during transportation. More specifically, the galvanized steel attachment strips are U-shaped and press fit around the ends of the expanded webbed steel cross members, which are also U-shaped. Frequently, during transportation, the press fit weakens, resulting in the loss of the galvanized steel attachment strips. This is unacceptable in a construction environment because of the resulting loss in time and material.
A related disadvantage is the loss of attachment that can occur under some circumstances. Specifically, the edges of expanded webbed steel cross members, if cut along metal crossing points, have V-shaped open areas between box-shaped closed areas. Anchors that fall in the V-shaped open areas are not laterally attached to the edges of the expanded webbed steel cross members. As a result, if all of the anchors attached to a solid galvanized steel strip fall in V-shaped areas, no lateral attachment to the associated expanded webbed steel cross member exists. As a result a lateral force, i.e., a force parallel to the wall, can detach the solid galvanized steel strip and anything affixed thereto from the associated expanded webbed steel cross member.
As will be better understood from the following discussion, the present invention overcomes the foregoing problems by providing interlocking concrete form modules that are structurally adequate and formed entirely of materials that are easy to cut to meet the comer requirements of construction jobs.